Decomposition of carbon-bearing compounds and their influence on methane formation in a lignite incubation experiment

Carbon-bearing compounds (glucose, sodium acetate, methanol, yeast extract, and nutrient broth) were added in different proportions to cultures to stimulate methanogenesis in a lignite incubation experiment. Their addition significantly influenced the isotopic composition of methane generated during the fermentation of lignite. Glucose was degraded mainly in the first 2 weeks of incubation, when the atmospheric air was present in the headspace and used for biomass growth. Sodium acetate, methanol, and, presumably, lignite were decomposed in the next phase, in which anaerobic conditions occurred. The simultaneous decomposition of sodium acetate and methanol (as single substrates or as a mixture) with lignite resulted in the formation of methane with δ13C(CH4) values typical for methyl-type fermentation. The identification of decomposed compounds in the mixture of sodium acetate and methanol was accomplished via isotopic analysis of carbon and hydrogen in the methane. The δ2H(CH4) values in the case of methanol biodegradation were characterized by a negative trend over time, in contrast to a positive trend observed when sodium acetate decomposed. This observation may help to identify a very good tracer for the determination of methane precursors during methyl-type fermentation.